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    Effect of La substitution on the microstructure and dielectric properties of the sol-gel derived BaZr0.2Ti0.8O3 thin films
    (ELSEVIER SCIENCE SA, 2016) Mahmood, Asad; Mensur-Alkoy, Ebru; Naeem, Abdul; Iqbal, Yaseen; Ullah, Asad; Alkoy, Sedat
    A-site deficient Ba1-xLa2x/3(Zr0.2Ti0.8)O-3 (BLZT) thin films with x = 0.00, 0.004, 0.006, 0.008, 0.02, 0.06 were processed using a sol-gel technique. X-ray diffraction analysis was used to investigate phase evolution of BLZT films with temperature. Scanning electron microscopy and atomic force microscopy were used to investigate the microstructure and surface topography of the fabricated BLZT thin films. The samples with x = 0.00-0.008 showed a homogeneous grain size distribution and uniform surface morphology; however, a certain degree of agglomeration was observed for the samples with x > 0.008 which increased with increasing La content. The magnitude of root mean square for the samples with x = 0.00, 0.004, 0.006, 0.008, 0.02 and 0.06 was recorded to be 3.53 nm, 3.06 nm, 2.32 nm, 2.02 nm, 3.36 nm and 4.71 nm, respectively. Relative permittivity (epsilon(r)) was observed to decrease with increasing temperature, and increased non-linearly with an increase in La content. Dielectric dispersion was observed for all the BLZT samples and er decreased with increasing frequency. (C) 2016 Elsevier B.V. All rights reserved.
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    Effect of powder processing conditions on the electromechanical properties of lithium doped potassium sodium niobate
    (ELSEVIER SCIENCE BV, 2016) Mensur-Alkoy, Ebru; Berksoy-Yauuz, Ayse
    Lithium doped potassium sodium niobate ceramics with (K0.50-x/2Na0.50-x/2Lix)NbO3 composition where x=0.04 and 0.07 were fabricated by solid state calcination and pressureless sintering methods. However, two different powder processing and calcination routes were used in this study and their effect on the structural and electrical properties were investigated and discussed. The routes were namely loose calcination and compact calcination. A general trend of decreasing grain size was observed in the sintered ceramics prepared from these powders. The most drastic effect was observed on the electromechanical properties of the samples, where the maximum strain of 7% lithium modified sample under an E-field of 50 kV/cm was increased from 0.09% to 0.12% by changing processing route. Furthermore, hysteretic behavior of the strain was found to decrease. This tendency was also valid for ferroelectric hysteresis property, with remnant polarization (2P(r)) increasing from 23 mu C/cm(2) to 46 mu C/cm(2). The improvements observed in the electrical properties were discussed on the basis of chemical homogeneity and uniform ionic distribution. (C) 2016 SECV. Published by Elsevier Espana,
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    Electrical Properties and Impedance Spectroscopy of Lithium Modified Potassium Sodium Niobate Ceramics
    (TAYLOR & FRANCIS LTD, 2013) Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Alkoy, Sedat
    Lead-free potassium sodium niobate (KNN) ceramics were prepared with lithium and tantalum modification. Structural properties were investigated. Impedance spectroscopy was used as a tool to analyze electrical behavior of ceramics as a function of frequency from 100Hz to 10MHz at a temperature range from 573K to 798K. Neither Li nor Li + Ta modification caused any secondary grain boundary phase, however both of them caused a densification of the ceramic. Increasing the lithium addition was found to decrease the impedance, while the Li + Ta addition drastically increased it. Finally, a temperature induced relaxation process was observed in the samples with the relaxation frequency shifting with temperature.
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    Fabrication of textured lead-free strontium barium niobate (SBN61) bulk ceramics and their electrical properties
    (ELSEVIER SCI LTD, 2016) Dursun, Sinan; Mensur-Alkoy, Ebru; Alkoy, Sedat
    Sr0.61Ba0.39Nb2O6 (SBN61) ceramic fibers with a high [001] texture were fabricated by a combination of alginate gelation method and templated grain growth process using acicular Ba2NaNb5O15 (BNN) template particles. The rod-like BNN template particles were prepared by molten salt synthesis method with salt/powder ratio of 2 giving the highest aspect ratio. Fibers were drawn from alginate based slurries without or with 10 wt% BNN template particles. Increasing sintering temperature and time were found to increase the texture. Textured SBN61 bulk ceramics with dimensions in cm scale were fabricated by wet packing a limited number of grain oriented green fibers and sintering the green bulk to obtain a dense, textured bulk ceramic through templated grain growth. A maximum texture fraction, f, of 0.91 was obtained, as measured by Lotgering factor. Increased remnant polarization and electromechanical properties were obtained as a result of this preferred grain orientation. (C) 2016 Elsevier Ltd. All rights reserved.
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    Growth of NBT template particles through topochemical microcrystal conversion and their structural characterization
    (WILEY, 2017) Dursun, Sinan; Mensur-Alkoy, Ebru; Sabuncu, Abdulsamet; Berksoy-Yavuz, Ayse; Gulgun, Mehmet Ali; Alkoy, Sedat
    In this study, uniform rectangular plate-like perovskite Na0.5Bi0.5TiO3 templates were obtained by molten salt synthesis method in three steps. Perovskite plate-like Na0.5Bi0.5TiO3 templates were synthesized from bismuth-layered Na0.5Bi4.5Ti4O15 by topochemical microcrystal conversion method at the third and final step. The most important point was that the plate-like morphology remained as desired, but templates were obtained in cubic perovskite structure. The Na2CO3 excess in the third step was the main controlling parameter. The crystalline orientation of the particles was investigated by electron backscatter diffraction analysis. The results indicated that the particles are single crystalline in nature. In the case of the 90mol% excess of the stoichiometric Na2CO3 ratio, the NBT platelets had highly regular, rectangular prismatic morphology and single-crystal nature. The structure was also confirmed through high-resolution transmission electron microscope and selected area electron diffraction analysis.
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    Macro and Microstructural Engineering of Piezoelectric Ceramics
    (TAYLOR & FRANCIS LTD, 2013) Alkoy, Sedat; Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Dursun, Sinan; Olukkent, Recep; Ozeren, Yagiz
    Dimension, shape and materials' properties are the most basic characteristics of a piezoelectric ceramic transducer determining the device performance. In our studies better electromechanical performance was obtained from piezoelectric ceramic itself by creating designs based on built-in amplification mechanisms obtained through the shape and geometry of the transducer, i.e. the macroscale engineering. Piezoceramics in thin hollow shell and fiber forms were fabricated by slip casting and alginate gelation. Additionally, improving materials properties along preferred directions can be achieved through the fabrication of crystallographically textured piezoceramics, i.e. Microscale Engineering. Alginate gelation and templated grain growth was used to produce them.
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    Processing and Properties of Textured Potassium Sodium Niobate [K,Na]NbO3 Ceramic Ribbons by Alginate Gelation Method
    (WILEY-BLACKWELL, 2014) Mensur-Alkoy, Ebru; Berksoy-Yavuz, Ayse; Alkoy, Sedat
    Random and < 001 > textured potassium sodium niobate - [K,Na]NbO3 (KNN) ceramics with 1 mole% CuO sintering aid were fabricated in ribbon form through a combination of novel alginate gelation process and templated grain growth methods using platelike sodium niobate - NaNbO3 (NN) template particles. The platelike NN template particles were prepared by a two-step molten salt synthesis method. Ribbons were drawn from alginate-based slurries without or with 10 wt% NN template particles using 50mm long slit nozzle with a rectangular orifice of 10mmx1mm. Development of crystallographic texture as a result of varying sintering time and temperature was evaluated through the calculation of the degree of orientation as measured by the Lotgering factor (integral((001))) and an integral((001)) of 0.81 was achieved. The electrical properties of textured ribbons were evaluated with polarization and strain versus electric field measurements.
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    Properties of [Pb(Zn1/3Nb2/3)O-3](x)-[Pb(Zr0.48Ti0.52)O-3]((1-x)) Ceramics With Low Sintering Temperature and Their 1-3 Piezocomposites
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016) Mensur-Alkoy, Ebru; Kaya, Mustafa Yunus; Avdan, Duygu; Alkoy, Sedat
    In this paper, dense (x)PZN-(1 - x)PZT ceramics were prepared at sintering temperatures as low as 950 degrees C with PZN ratios of x = 0.4, 0.5, and 0.6. The 0.4PZN-0.6PZT composition was found to crystallize in the perovskite phase at this sintering temperature without the presence of any other secondary phases. Higher electrical and electromechanical properties were obtained from the 0.4PZN-0.6PZT composition compared with the x = 0.5 and x = 0.6 counterparts. Dielectric constant, piezoelectric charge coefficient, electromechanical coupling coefficient, and mechanical quality factor of 0.4PZN-0.6PZT were found to be 2608, 477 pC/N, 64.4, and 65, respectively. While the Curie temperature was 140 degrees C for pure PZN, the Curie temperature was measured as 300 degrees C for x = 0.4 composition. Green PZN-PZT fibers with circular cross section were drawn using alginate gelation method from the 0.4PZN-0.6PZT composition. Dense fibers were obtained after the sintering process, and piezocomposites were prepared with 1-3 connectivity using fibers with an average diameter of 600 mu m. Composites with volume fraction of 20 vol% were investigated for passive acoustic sensor applications. Electrical properties of piezocomposites were found to be scalable and compatible with the electrical properties of the bulk composition. The dielectric constant, piezoelectric charge coefficient, and maximum strain value of the PZN-PZT 1-3 piezocomposite were measured as 345, 165 pC/N, and 0.13%, respectively.
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    Sodium niobate particles with controlled morphology synthesized by hydrothermal method and their use as templates in KNN fibers
    (ELSEVIER SCIENCE BV, 2014) Ozeren, Yagiz; Mensur-Alkoy, Ebru; Alkoy, Sedat
    Sodium niobate - NN (NaNbO3) powders were synthesized by hydrothermal process to be used as template particles in the fabrication of textured lead free piezoelectric ceramics. Sodium hexaniobate-Na8Nb6O19 center dot 13H(2)O particles with rod-like morphology were synthesized at 120 degrees C. Particles with needle-like morphology and Na-2(Nb2O6)(H2O) phase started to form at temperatures of 130 degrees C and above. Synthesis at 150 degrees C yields particles with totally needle-like morphology and consisting entirely of the Na-2(Nb2O6)(H2O) phase. Sodium niobate-NaNbO3 particles with cubic morphology were synthesized at temperatures of 160 degrees C and above. Rod-like and needle-like morphology was retained even after annealing at 400 degrees C for 1 h. A preliminary study was also done to integrate these anisometric template particles in the preparation of textured potassium sodium niobate (KNN) fibers. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.